Oxidation of glycols

ABSTRACT

PROCESS FOR PREPARING MONOCARBOXYLIC ACIDS FROM GLYCOLS WHEREBY THE FORMATION OF MONOCARBOXYLIC ACID IS FAVORED AND THE FORMATION OF DICARBOXYLIC ACID IS SUBSTANTIALLY SUPPRESSED. THE PROCESS COMPRISES OXIDIZING NEOPENTYL GLYCOL, ETHYLENE GLYCOL, AND POLYETHYLENE GLYCOLS CONTAINING FROM 2 TO 8 ETHYLENE GLYCOL UNITS TO THE CORRESPONDING MONOCARBOXYLIC ACID, IN THE PRESENCE OF AN OXYGEN CONTAINING GAS AND A SUPPORTED PLATINUM METAL OXIDATION CATALYST, WHILE ADDING A SUITABLE BASE TO MAINTAIN THE PH OF THE REACTION MIXTURE WITHIN THE RANGE OF 6.5 TO 9.

United States Patent Ofice Patented Mar. 26, 1974 3,799,977 OXIDATION OF GLYCOLS Thomas F. Rutledge, Wilmington, Del., assignor to ICI America Inc., Wilmington, Del. No Drawing. Filed Jan. 28, 1972, Ser. No. 221,801 Int. Cl. C07c 51/26, 53/22 U.S. Cl. 260-531 R 3 Claims ABSTRACT OF THE DISCLOSURE Process for preparing monocarboxylic acids from glycols whereby the formation of monocarboxylic acid is favored and the formation of dicarboxylic acid is substantially suppressed. The process comprises oxidizing neopentyl glycol, ethylene glycol, and polyethylene glycols containing from 2 to 8 ethylene glycol units, to the corresponding monocarboxylic acid, in the presence of an oxygen containing gas and a supported platinum metal oxidation catalyst, while adding a suitable base to maintain the pH of the reaction mixture within the range of 6.5 to 9.

This invention relates to a process for the preparation of monocarboxylic acids. More particularly, this invention relates to an improved process for the preparation of monohydroxy monocarboxylic acids by the catalytic oxidation of glycols.

The preparation of carboxylic acids by the catalytic oxidation of hydroxyl containing organic compounds is well known in the prior art. While many satisfactory processes are known for the oxidation of monohydric a1- cohols to the corresponding carboxylic acid, these processes have not been satisfactory when applied to the preparation of monocarboxylic acids by the catalytic oxidation of glycols. The use of such processes to oxidize glycols has not been satisfactory because they result in the oxidation of both hydroxyl groups to form dicarboxylic acids, or at best, these processes result in the formation of a mixture of dicarboxylic acid and a small amount of monocarboxylic acid. Processes for the oxidation of glycols are also known in the prior art as shown by Heyns and Blazejewicz, Tetrahedron 9, 67-75 (1960). These prior art processes have not been satisfactory because they result in low yields of the monocarboxylic acid or in the formation of substantial amounts of dicarboxylic acids. It would be highly desirable to provide a simple, economical, and eflicient method for preparing monohydroxy monocarboxylic acids by the selected oxidation of only one hydroxyl group of a glycol.

Accordingly, it is an object of the present invention to provide a novel and improved process for preparing monohydroxy monocarboxylic acids. Another object of this invention is to provide a process for the selective oxidation of glycols whereby only one of the hydroxyl groups present in the glycol is oxidized to a carboxyl group. Another object of this invention is to minimize formation of dicarboxylic acids during the oxidation of glycols. Another object is to provide a simple, economical, elficient and commercially attractive process for preparing monocarboxylic acids containing one free hydroxyl group by the catalytic oxidation of glycols.

The foregoing objects and still further objects of this invention are broadly accomplished by providing an improved process for the preparation of monocarboxylic acid from a glycol selected from the group consisting of neopentyl glycol, ethylene glycol and polyethylene glycols containing from 2 to 8 ethylene glycol units, whereby one of the hydroxyl groups of the glycol is oxidized to a carboxyl group and the other hydroxyl group of the glycol is left unmodified, which process comprises oxidizing the glycol in the presence of an oxygen containing gas and a supported platinum metal catalyst while maintaining the pH of the reaction mixture within the range of 6.5 to 9. It has been discovered in accordance with the present invention that in the catalytic oxidation of neopentyl glycol, ethylene glycol or polyethylene glycols containing from 2 to 8 glycol units to the corresponding monocarboxylic acid, improved yields of the monocarboxylic acid may be obtained and the formation of dicarboxylic acid substantially suppressed by maintaining the pH of the reaction solution from 6.5 to 9.

In carrying out the process of the present invention it is essential that the pH of the reaction mixture be maintained throughout the course of the reaction at a value from 6.5 to 9. It has been found quite unexpectedly that if the pH of the reaction mixture is allowed to increase above 9, the ratio of monocarboxylic acid to dicarboxylic acid starts to decrease rapidly. The yield of monocarboxylic acid decrease rapidly at pH values below 6.5. Accordingly, in order to obtain the highest yields of the corresponding monocarboxylic acid and to suppress the formation of the corresponding dicarboxylic acid, the pH must be maintained within a range from about 6.5 to 9, and preferably below 9, throughout the entire course of the oxidation reaction. The pH of the reaction mixture may be maintained from 6.5 to 9 by any convenient means. A preferred means comprises adding alkaline material to the reaction mixture during the course of the oxidation reaction to maintain the pH from 6.5 to 9. A preferred class of alkaline material are the metal hydroxides, including the alkali and alkaline earth metal hydroxides. A preferred hydroxide is sodium hydroxde.

The catalyst employed in the oxidation process of the present invention may be any of the platinum metal catalysts which are conventionally used in the art for the catalytic oxidation of alcohols to carboxylic acids. The platinum catalysts may be supported on an inert catalyst carrier material which provides a sufiiciently large surface area for the platinum deposited thereon. Illustrative examples of such well known catalysts support are finely divided carbon, silica and kieselguhr. The amount of platinum supported on the carrier is not critical and is usually from 1% to 15%, and preferably about 3% to 10%, of platinum based on the total weight of catalyst.

The amount of supported platinum catalyst employed in the process of the present invention should be that amount which is sufiicient to provide a catalytic effect. In most cases, the amount of catalyst used is from 0.2 gram of supported catalyst per millimols of glycol to 1 gram of supported catalyst per gram of glycol. It will be understood, of course, that smaller and larger amounts of catalyst may be used if desired.

The catalyst may be employed in the form of a stationary bed positioned in a suitable reaction zone providing for intimate contact between reactants and catalysts. Suitable reaction zones may comprise one or more chambers of enlarged cross-sectional area, reaction zones of restricted cross-sectional areas, such as tubular reactors, or combinations thereof. The process particularly lends itself to being carried out with the catalyst slurried in an aqueous solution of the glycol.

The reaction is carried out at any temperature which gives a satisfactory rate of reaction and which does not result in a substantial amount of undesirable side reactions and may be any of the temperatures used in the art for the oxidation of hydroxy groups to carboxy groups. A particularly preferred temperature range is from 20 to 70 C.

With the exception of the pH of the reaction mixture, which must be maintained from 6.5 to 9, the reaction conditions, such as temperature, catalyst concentration, concentration of platinum on the carrier, nature of the carrier, etc., form no part of this invention and may be 3 any of the reaction conditions which are used in the art for the oxidation of hydroxyl groups to carboxyl groups. The following examples are illustrative of preferred processes of this invention. These examples are set forth acid (92 millimols). The total conversion to glycolic acid is 87%.

EXAMPLE 3 53 grams of diethylene glycol, 3.8 grams of a 5% solely for the purpose of illustration and any specific 5 4 d enumeration of details contained therein should not be glg i g f gg gg gg 323 igimiz z ggggsg x ii; interpreted as expressing limitations of this invention. It are charged to tlfle reactor described in Example 1. Air will 7 readlly.apparent to those Sklned m h art that is removed by flushing the reactor with oxygen for 45 reaction conditions such as solvent, concentrations, cataminutes The reactor is then closed and heated to 400 y t may be altered for those rented 10 over a 10 minute period. A 4.1 N sodium hydroxide solum followmg examp All parts and Percentages are tion is added to maintain the pH of the reaction mixture by welght unless otherwlse Stated at 8.5 while oxygen is consumed. After 3.5 hours, oxygen consumption is 12.6 liters (562 millimols) and base EXAMPLE 1 consumption is 125 milliliters 513 millimols). Oxidation The reactor employed is a cylindrical stirred vessel, 53 33 gggiit ligfigi z gg g igzgg gg gfiig gsgfi fitted with a smtered glass dlsc for-spargmg Oxygen-gas action mixture to room temperature The catalyst is rem very fine bubbles through the surfed lgly-c o1 Solutloni moved b filterin The filtrate has a H of 8 1 Anal sis catalyst suspension. An external Pump recirculates (the of an gq solution shows 5 14% wire gfg fig g f i fig gg 'f f g fi g gfi g jg sponding to 3 millimols of co per 100 millimols of dieflbove algmospheil'lic prtlelssurle. sodiulilll hygri f i 2 51: di v fil l ii ti ii a sni i 21 113 digs l jz rom a urettet roug a ong nee e w 1c ex en s mo the reactor below the surface of the liquid. Temperature fg g g g zg fi g gggi ggg a f n z gg g sjg is controlled by a thermistor device. T

6.2 grams of ethylene glycol is dissolvedbm 160 ml. 05 25 22522 22 2 g 1 gg g g g sfig g g gi g 322 53 s sgz g ggf gfi i g ag fit gggzgi sure to remove water and most of the acetic acid. The 2 platinum based on the total weight of platinum and residue is a slightly viscous liquid, clear and colorless. carbon. The glycol solution-catalyst suspension is placed g g gi g gg ggggz :3 gi z i l z i g gi g g 22 5: in the reactor, and air is removed by flushing with oxyd th y y .gen for 45 minutes. The contents of the reactor are ece ereac mlx stirred and heated to 50 C. The oxygen pressure is main- EXAMPLE 4 tained at 5 mm. above atmospheric and oxygen consump- 31 3 ams of neo ent 1 1 col, 300 millillters of derficordfad i 5 mmute Intervals The the 35 ionized water, and 2 grai ms Zf a 5% platinum-carbon sohmqn 1S mFImtamed bqween i 9 bypontmuousl catalyst are placed in the reactor described in Example ly adding sodium hydroxide to maintaln a sodium hydrox- 1 Air is removed by purging with oxygen for 45 ide/oxygen consume? ram) of to (111018) utes. Temperature is then adjusted to 60 C., and 4.2 N 5 g i s z i 3; gfi i ig sodium hydroxide solution is added to maintain a pH of mo S so mm y e an m1 m0 S o y? 40 8.5. After reaction for 5 hours, oxygen consumption is mllhmols of oxygqn 1s consum.ed after base addmon 314 millimols and the sodium hydroxide consumption is Is Stopped) The reactlon product 18 filtered and h 211 millimols. The catalyst is removed by filtration. The filtratg has fi 3 :52:: i gg f: m filtrate weighs 355.7 grams and analysis thereof indicates accor ance W e proce u e p that neopentyl glycol had been converted to the monoacid of neopentyl glycol. EXAMPLE 2 Additional examples showing the preparation of monocarboxylic acids of various glycols in accordance with the Example 1 repeatefi Fxcept that the amount of process of the present invention are shown in the followgen Consumed {111111111015 'f the amount of sPdlum ing Table I. The reactor and reaction and process procehydrOXide p y 1S mllll'mols Over a Perlod of dure employed in the following examples was identical 1.66 hours. The pH Of the filtrate is 8.5. This filtrate and to that employed in Example 1, The pH of the reaction the filtrate from Example 1 are combined and the pH mixture is maintained at a value from 6.5 to 9 during adjusted to 4 by the addition of hydrochloric acid. The the oxidation reaction.

TABLE I Grams 01- Percent mono- Example 5% Pt- Tempera- Mmols Mmols acid in Number Glycol Glycol carbon ture, C. Time of O of NaOH product 5 Ethylene 9.3 0.5 30 1% 150 135 so 6. Triethylene 28.1 1.9 50 3 329 331 97 7. Tetraethylene....- 36.4 1.95 in 187.5 185.5 89 8 Hexaethylene 56.2 1.95 60 2 134 136 1 Amount; of monoacid in product not determined.

resulting solution is then evaporated to a volume of 180 The above examples and description areto be taken milliliters and passed through a column of strong base as only illustrative of the invention and a number of its ion exchange resin in the hydroxyl form (Dowex 21A). The first fraction of eluate, eluted with Water, contains 7.9 grams of sodium glycolate (91 millimols), identified by infrared analysis. The second fraction of eluate, eluted preferred embodiments and it is to be understood that many further variations and modifications of the invention may be made by those skilled in the art without departing from the scope and spirit of the invention which with dilute hydrochloric acid, contains 7 grams of glycolic is defined in the appended claims.

Having thus described the invention, what is desired to be secured by Letters Patent is:

1. In a process for the preparation of monohyoroxy monocarboxylic acids by oxidizing a polyethylene glycol containing from 2 to 8 ethylene glycol units, in the presence of an oxygen containing gas and a supported platinum metal catalyst, the improvement which comprises maintaining the pH of the reaction mixtures within the range of 6.5 to 9.

2. A process of claim 1 wherein the pH of the reaction mixture is maintained within the range of 6.5 to 9 by adding a base to the reaction mixture during the course of the oxidation reaction.

3. The process of claim 2 wherein the base employed is sodium hydroxide.

References Cited UNITED STATES PATENTS LORRAINE R. WEINBERGER, Primary Examiner R. D. KELLY, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE. OF CORRECTION PATENT NO. I 3,799,977

DATED 1 March 26 1974 OM Thomas F. Rutledge, Wilmington, DE

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 31, "hydroxde" should read hydroxide Column 5, line 9, "mixtures" should read mixture Signed and Scaled this second Day of December1975 [SEAL] Attest:

RUTH (I. MASON C. IARSIIALL DAMN Arresting Officer Commissioner nfPntems and Trademarks 

